In a packet switched or packet mode computer network, data is transmitted in the form of packets (sometimes referred to as datagrams, segments, blocks, cells or frames) according to predefined protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP). A sequence of packets transmitted from a source to a destination is referred to as a network flow.
Packets generally contain control information and actual data (also known as payload). The control information is data that network devices use to forward the packet from a source to a destination, and may comprise, for example, source and destination addresses, error detection codes (i.e., checksums), sequencing information, etc. This control information is generally found in a portion of the packet referred to as the packet header (i.e., the information that precedes the actual data within the packet) and/or the packet trailer (i.e., the information that follows the actual data within the packet). Packets are routed in the network on the basis of this control information.